Self-dispersing, hardenable epoxy resins, processes for producing the same and methods of using the same

ABSTRACT

Self-dispersing, hardenable epoxy resins produced by reacting one or more α,β-unsaturated carboxylic acid esters with one or more aminopolyalkylene oxide compounds, and reacting the thus formed intermediate with one or more polyepoxide compounds, are described. Processes for their production, aqueous dispersions containing the same and methods for their use are also described.

FIELD OF THE INVENTION

This invention relates to self-dispersible curable epoxy resins and to aprocess for their production. The epoxy resins according to theinvention are special compounds based on α,β-unsaturated carboxylic acidesters. The present invention also relates to aqueous dispersionscontaining these special epoxy resins. Finally, the invention relates tothe use of these special epoxy resins for coating solid substrates.

PRIOR ART

For many years, curable epoxy resins have been used as components incoating compositions. However, the properties of coatings produced usingaqueous epoxy resin dispersions have long been considered inferior tothose of coatings in which the resin is used in the form of a solutionin an organic solvent. This was mainly attributed to the fact that theemulsifiers used, for example nonylphenol ethoxylates, migrate to thesurface of the film where they adversely affect its properties. One wayof solving this problem is to use so-called reactive emulsifiers which,where the epoxy resin is crosslinked with a diamine or polyamine orother hardener, react with the hardener and thus become part of thecoating. Aqueous dispersions of special reactive emulsifiers are knownfrom the prior art.

U.S. Pat. No. 4,315,044 describes a stable epoxy resin dispersioncontaining (1) an aqueous medium and (2) between 50 and 70% by weight ofa self-emulsifiable epoxy resin which is the addition product of (a) 40to 90% by weight of diglycidyl ethers of a dihydric phenol, (b) 5 to 35%by weight of a dihydric phenol and (c) 2 to 15% by weight of thediglycidyl ether of a polyoxyalkylene glycol and in which the molecularweight of the epoxy resin is between 500 and 20,000.

U.S. Pat. No. 4,608,406 describes a stable epoxy dispersion containing(1) an aqueous medium and (2) between 50 and 70% by weight of aself-emulsifiable epoxy resin with a molecular weight of 1,000 to 20,000which is the addition product of (a) 40 to 90% by weight of diglycidylethers of a dihydric phenol, (b) 5 to 35% by weight of a dihydricphenol, (c) 2 to 15% by weight of the diglycidyl ether of apolyoxyalkylene glycol and (d) 2 to 15% by weight of an alkylphenol/formaldehyde/novolak resin.

EP-B-272 595 and DE-A-36 43 751 describe a process for the productionand use of stable aqueous epoxy resin dispersions consisting of a) 50 to80% by weight of an epoxy compound containing at least two epoxy groupsper molecule and having an epoxy equivalent weight of 100 to 2,000, b)35 to 17% by weight of an aromatic polyol and c) 15 to 3% by weight of acondensation product of an aliphatic polyol with a molecular weight (Mw)of 200 to 20,000 and an epoxy compound containing at least two epoxygroups per molecule and having an epoxy equivalent weight of 100 to2,000, the equivalent ratio of the OH groups to the epoxy groups beingfrom 1:0.85 to 1:3.5 and the epoxy equivalent weight of thiscondensation product being from 200 to at least 50,000.

WO 95/18165 (Henkel Corp.) describes a self-dispersible curable epoxyresin obtainable by reacting an epoxy resin (a) with a polyoxyalkyleneamine (b) with a molecular weight of 3,000 to 15,000. The componentsmentioned are used in a ratio of (b) to (a) of 0.001:1.0 to 0.060:1.0equivalent.

WO 96/20970 (Henkel Corp.) describes a self-dispersible curable epoxyresin obtainable by reacting (a) 1.0 equivalent of epoxy resin, (b) 0.01to 1.0 equivalent of a polyhydric phenol and (c) 0.005 to 0.5 equivalentof an amine/epoxy adduct. The amine/epoxy adduct is a reaction productof 1.0 equivalent of a polyepoxide and 0.3 to 0.9 equivalent of apolyoxyalkylene diamine.

EP-A-747 413 describes a self-emulsifiable epoxy resin (A) obtainablefrom (A-1) 50 to 95% by weight of one or more epoxy compound(s)containing at least two epoxy groups per molecule and having an epoxygroup content of 300 to 11,200 mmoles/kg, (A-2) 5 to 50% by weight of anaromatic polyol, (A-3) 0 to 25% of modifying compounds containing atleast two epoxy-reactive groups, (A-4) 5 to 35% of a condensationproduct—acting as emulsifier—of (A-4-a) an aliphatic polyol with aweight average molecular weight M_(w) of 200 to 20,000 g/mole and(A-4-b) an epoxy compound containing at least two epoxy groups permolecule and having an epoxy group content of 500 to 10,000 mmoles/kg,the ratio of the number of OH groups to the number of EP groups beingfrom 1:2 to 1:10 and the epoxy group content of the condensationproducts (A-4) being from 100 to 6,700 mmoles/kg.

DESCRIPTION OF THE INVENTION

The problem addressed by the present invention was to provideself-dispersible curable epoxy resins. The expression “self-dispersible”in the context of the present invention means that the epoxy resins canbe dispersed or emulsified spontaneously in aqueous medium without theuse of additional additives, such as emulsifying or dispersingadditives. In other words, the epoxy resins to be developed are thosewhich would be capable of self-dispersion and/or self-emulsification inwater. In the interests of simplicity, the term “self-dispersing” isused for this property throughout the present specification. Anotherproblem addressed by the invention was to provide aqueous dispersions ofself-dispersible curable epoxy resins which would be distinguished byhigh stability in storage under practical storage conditions. A furtherproblem addressed by the invention was to provide coating compositionscontaining a self-dispersible curable epoxy resin, the coating obtainedfrom the coating composition after the curing process beingdistinguished by excellent properties.

It has now surprisingly been found that epoxy resins obtainable byreaction of α,β-unsaturated carboxylic acid esters with mono-, di- orpolyaminopolyalkylene oxide compounds and subsequent reaction of theintermediate product obtained with an epoxy resin known from the priorart excellently satisfy the requirements mentioned in every respect.

The present invention relates first to self-dispersible curable epoxyresins obtainable by

-   -   (a) reacting one or more α,β-unsaturated carboxylic acid esters        (I)        R²R³C═C(R⁴)COOR¹   (I)        -   where R¹ is an aromatic or aliphatic radical containing up            to 15 carbon atoms, the substituents R², R³ and R⁴            independently of one another represent hydrogen, branched or            unbranched, aliphatic or aromatic groups containing up to 20            carbon atoms or a group —(CH₂)_(n)—COOR¹, where R¹ is as            defined above and n is a number of 0 to 10, with    -   (b) one or more mono-, di- or polyaminopolyalkylene oxide        compounds, compounds (a) and (b) being used in such quantities        that the equivalent ratio of the reactive hydrogen atoms at the        aminonitrogen atoms of (b) to the C═C double bond in the        α,β-position to the group COOR¹ shown in formula (I) in the        carboxylic acid esters (a) is in the range from 10:1 to 1:10,    -   and subsequently reacting the intermediate product obtained with    -   (c) one or more polyepoxides, the equivalent ratio of oxirane        rings in polyepoxide (c) to reactive hydrogen atoms of the        mono-, di- or polyaminopolyalkylene oxide compounds used in (b)        being adjusted to a value of 100:1 to 1.5:1.

The epoxy resins according to the invention are either liquid or solidsubstances, depending on their molecular weight.

The expression “equivalent ratio” is familiar to the expert. The basicconcept behind the notion of the equivalent is that, for every substanceparticipating in a reaction, the reactive groups involved in the desiredreaction are taken into consideration. By indicating an equivalentratio, it is possible to express the ratio which all the variousreactive groups of the compounds (x) and (y) used bear to one another.It is important in this connection to bear in mind that a reactive groupis understood to be the smallest possible reactive group, i.e. thenotion of the reactive group is not identical with the notion of thefunctional group. In the case of H-acid compounds, this means forexample that, although OH groups or NH groups represent such reactivegroups, NH₂ groups with two reactive H atoms positioned at the samenitrogen atom do not. In their case, the two hydrogen atoms within thefunctional group NH₂ are appropriately regarded as reactive groups sothat the functional group NH₂ contains two reactive groups, namely thehydrogen atoms. Example: if a compound (a) containing one olefinicdouble bond in the apposition to a carboxyl group per molecule isreacted with a compound (b) containing one NH₂ group per molecule by aMichael addition, compound (a) is regarded as containing one reactivegroup C═C per molecule whereas compound (b) is regarded as containingtwo reactive hydrogen atoms attached to the nitrogen. If, now, (a) and(b) were to be reacted in an equivalent ratio of 1:1, one mole of (a)would have to be reacted with half a mole of (b) because (b) does ofcourse contain two reactive groups per molecule. By contrast, for anequivalent ratio of (a) to (b) of 1:2, 1 mole of (a) would have to bereacted with 1 mole of (b). An equivalent ratio of, for example, (a) to(b) of 1:10 could of course also be adjusted although in that case 1mole of (a) would have to be reacted with 5 moles of (b). This wouldmean that component (b) would be used in excess because, of course, atmost 1 mole of component (b) could theoretically be reacted with (a) ina Michael addition.

So far as the compounds belonging to classes (a) to (c) are concerned,it is expressly pointed out that they are different substances.

In one embodiment, compounds (a) and (b) are used in such quantitiesthat the equivalent ratio of reactive hydrogen atoms at theaminonitrogen atoms of (b) to the C═C double bond in the α,β-position tothe group COOR¹ in formula (I) in the carboxylic acid esters (a) is inthe range from 4:1 to 1:4 and more particularly in the range from 2.5:1to 1.5:1.

In another embodiment, the equivalent ratio of oxirane rings in thepolyepoxide (c) to reactive hydrogen atoms of the mono-, di- orpolyaminopolyalkylene oxide compounds used in (b) is adjusted to a valuein the range from 100:1 to 1.5:1.

Examples of the α,β-unsaturated carboxylic acid esters (a) correspondingto formula (I) to be used in accordance with the invention are methylacrylate, ethyl acrylate, dimethyl maleate, diethyl maleate, dimethylfumarate, diethyl fumarate, dimethyl itaconate, diethyl itaconate.Particularly preferred compounds (a) are dialkyl maleates, moreparticularly diethyl maleate and dimethyl maleate.

Suitable amino components (b) are mono-, di- or polyaminopolyalkyleneoxide compounds. By this is meant that these compounds contain on theone hand one, two or more amino functions (NH or NH₂ functions) and, onthe other hand, alkylene oxide units. The alkylene oxide units are, inparticular, ethylene oxide, propylene oxide and butylene oxide, ethyleneoxide and propylene oxide being particularly preferred. The compounds(b) are substances at least partly soluble in water at 20° C.

The production of the compounds (b) is known from the prior art andcomprises the reaction of hydroxyfunctional compounds with alkyleneoxides and subsequent conversion of the resulting terminal hydroxylgroups into amino groups.

So far as the reaction of hydroxyfunctional compounds with alkyleneoxides is concerned, ethoxylation and propoxylation are of particularimportance. The following procedure is usually adopted: in a first step,the required hydroxyfunctional compounds are contacted with ethyleneoxide and/or propylene oxide and the resulting mixture is reacted in thepresence of an alkaline catalyst at temperatures in the range from 20 to200° C. Addition products of ethylene oxide (EO) and/or propylene oxide(PO) are obtained in this way. The addition products are preferably EOadducts or PO adducts or EO/PO adducts with the particularhydroxyfunctional compound. In the case of the EO/PO adducts, theaddition of EO and PO may be carried out statistically or blockwise.

In one embodiment, substances with the general formulaR⁸—O—R⁹—CH₂CH(R¹⁰)—NH₂ are used as the compounds (b). In this formula:

-   -   R⁸ is a monofunctional organic group containing 1 to 12 carbon        atoms which may be aliphatic, cycloaliphatic or aromatic,    -   R⁹ is a polyoxyalkylene group made up of 5 to 200        polyoxyalkylene units, more particularly EO and/or PO units,    -   R¹⁰ is hydrogen or an aliphatic radical containing up to 4        carbon atoms.

Particularly suitable representatives of the compounds (b) for thepurposes of the present invention are the “Jeffamines” known to theexpert which are commercially available substances. One example is“Jeffamine 2070” which, according to the manufacturer Texaco, isproduced by reacting methanol with ethylene oxide and propylene oxideand then converting the terminal hydroxyl groups of the intermediateproduct initially obtained into amine groups (cf. WO 96/20971, page 10,lines 12-15).

The compounds (b) preferably have average molecular weights (numberaverage Mn) of 148 to 5,000 and more particularly in the range from 400to 2,000.

The epoxy compounds (c) are polyepoxides containing on average at leasttwo epoxy groups per molecule. These epoxy compounds may be bothsaturated and unsaturated and aliphatic, cycloaliphatic, aromatic andheterocyclic and may also contain hydroxyl groups. They may also containsubstituents which do not cause any troublesome secondary reactionsunder the mixing and reaction conditions, for example alkyl or arylsubstituents, ether groups and the like. These epoxy compounds arepreferably polyglycidyl ethers based on polyhydric, preferably dihydricalcohols, phenols, hydrogenation products of these phenols and/ornovolaks (reaction products of mono- or polyhydric phenols withaldehydes, more particularly formaldehyde, in the presence of acidiccatalysts). The epoxy equivalent weights of these epoxy compounds arepreferably between 160 and 500 and more preferably between 170 and 250.The epoxy equivalent weight of a substance is the quantity of thesubstance (in grams) which contains 1 mole of oxirane rings. Preferredpolyhydric phenols are the following compounds: resorcinol,hydroquinone, 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A), isomermixtures of dihydroxydiphenyl methane (bisphenol F), tetrabromobisphenolA, 4,4′-dihydroxydiphenyl cyclohexane,4,4′-dihydroxy-3,3-dimethyldiphenyl propane, 4,4′-dihydroxydiphenyl,4,4′-dihydroxybenzophenol, bis-(4-hydroxyphenyl)-1,1-ethane,bis-(4-hydroxyphenyl)-1,1-isobutane, bis-(4-hydroxyphenyl)-methane,bis-(4-hydroxyphenyl)-ether, bis-(4-hydroxyphenyl)-sulfone etc. and thechlorination and bromination products of the above-mentioned compounds.Bisphenol A is most particularly preferred.

The polyglycidyl ethers of polyhydric alcohols are also suitablecompounds (c). Examples of such polyhydric alcohols are ethylene glycol,diethylene glycol, triethylene glycol, 1,2-propylene glycol,polyoxypropylene glycols (n=1-20), 1,3-propylene glycol, 1,4-butyleneglycol, pentane-1,5-diol, hexane-1,6-diol, hexane-1,2,6-triol, glyceroland bis-(4-hydroxycyclohexyl)-2,2-propane.

Other suitable compounds (c) are polyglycidyl ethers of polycarboxylicacids obtained by reaction of epichlorohydrin or similar epoxy compoundswith an aliphatic, cycloaliphatic or aromatic polycarboxylic acid, suchas oxalic acid, succinic acid, adipic acid, glutaric acid, phthalicacid, terephthalic acid, hexahydrophthalic acid,2,6-naphthalenedicarboxylic acid and dimerized linolenic acid. Examplesare adipic acid diglycidyl ester, phthalic acid diglycidyl ester andhexahydrophthalic acid diglycidyl ester.

A comprehensive list of suitable epoxy compounds (c) can be found in:

-   -   A. M. Paquin, “Epoxidverbindungen und Epoxidharze”,        Springer-Verlag, Berlin 1958, Chapter V, pages 308 to 461 and    -   Lee, Neville “Handbook of Epoxy Resins” 1967, Chapter 2, pages        201 and 2-33.

Mixtures of several epoxy compounds (c) may also be used,

The present invention also relates to a process for the production ofself-dispersible curable epoxy resins comprising the steps of

-   -   (a) reacting one or more α,β-unsaturated carboxylic acid esters        (I)        R²R³C═C(R⁴)COOR¹   (I)        -   where R¹ is an aromatic or aliphatic radical containing up            to 15 carbon atoms, the substituents R², R³ and R⁴            independently of one another represent hydrogen, branched or            unbranched, aliphatic or aromatic groups containing up to 20            carbon atoms or a group —(CH₂)_(n)—COOR¹, where R¹ is as            defined above and n is a number of 0 to 10, with    -   (b) one or more mono-, di- or polyaminopolyalkylene oxide        compounds, compounds (a) and (b) being used in such quantities        that the equivalent ratio of the reactive hydrogen atoms at the        aminonitrogen atoms of (b) to the C═C double bond in the        α,β-position to the group COOR¹ shown in formula (I) in the        carboxylic acid esters (a) is in the range from 10:1 to 1:10,    -   and subsequently reacting the intermediate product obtained with    -   (c) one or more polyepoxides, the equivalent ratio of oxirane        rings in polyepoxide (c) to reactive hydrogen atoms of the        mono-, di- or polyaminopolyalkylene oxide compounds used in (b)        being adjusted to a value of 100:1 to 1.5:1.

The present invention also relates to aqueous dispersions the containingthe self-dispersible curable epoxy resins according to the invention.The content of the epoxy resins according to the invention in thesedispersions is between 40 and 70% by weight, based on the dispersion asa whole.

In many cases, aqueous dispersions containing the epoxy resinsobtainable by the process according to the invention are distinguishedby very small mean particle sizes of around 500 nm or smaller. Thisleads to very favorable material properties of the coatings formed withthese dispersions. Particularly favorable material properties areobtained when the mean particle size is below about 300 nm. The meanparticle size is defined as the average of the particle sizes which isobtained by adding the values of n individual measurements and thendividing the total by n. For the purposes of the present invention, themean particle sizes were determined using a “Coulter N4 Plus SubmicronParticle Sizer” (manufacturer: Coulter, Miami, Fla. 33196, USA). Thisinstrument uses the scattering of laser light at a heavily diluteddispersion for particle size determination. It performs a number ofindividual measurements and gives the mean particle size as the endresult. The above-mentioned values relate to scattering measurements atan angle of 90° relative to the incident laser beam.

The self-dispersible curable epoxy resins according to the invention aresuitable in combination with suitable hardeners, more particularly theamine hardeners known to the relevant expert, and optionally othertypical additives for the production of coatings, intermediate coatings,paints, molding compositions and curable pastes for variousapplications. For example, they may be used for the production ofprotective and/or decorative coatings on various, above all rough andporous substrates such as, for example, wood, mineral substrates (forexample concrete and stone), glass, plastics (for example polyethylene,polypropylene), compost materials, ceramics and pretreated ornon-pretreated metals. Their favorable properties also make the epoxyresins according to the invention eminently suitable for one-coatlacquering/painting. The adhering coating layer may remain unchanged assuch although it may also serve as an intermediate layer, i.e. as asubstrate for further coatings which in turn may consist of the samecoating material or of another typical coating material.

Accordingly, the present invention also relates to the use of theself-dispersible curable epoxy resins according to the invention for theapplications mentioned.

By virtue of their good dilutability and their favorable properties,aqueous dispersions containing the epoxy resins according to theinvention are also suitable for use in electrodeposition painting.Aqueous dispersions containing the epoxy resins according to theinvention may also be used for the production of water-dilutableadhesives, as binders for textile, organic and/or inorganic materialsand as an additive in plastic cements.

EXAMPLES

In Examples 2, a “Coulter N4 Plus Submicron Particle Sizer”(manufacturer: Coulter, Miami, Fla. 33196, USA) was used to determinethe mean particle sizes. The measured values relate to scatteringmeasurements at an angle of 90° relative to the incident laser beam.

Example 1

17.5 g of diethyl maleate were added dropwise with stirring at 80° C. to200.0 g of monoaminopolyethylene oxide (“Jeffamine M 2070”, Huntsman),followed by stirring for another hour at 80° C. 380.0 g (0.3 mole) ofChemres E50 (bisphenol A-based epoxy resin of Henkel SpA, average epoxyequivalent weight ca. 475 g) were then added dropwise, followed bystirring for 1 hour at 100° C. The solvent was then removed in vacuo and570.0 g (1.5 moles) of Chemres E20 (bisphenol A-based epoxy resin ofHenkel SpA, average epoxy equivalent weight ca. 190 g) and—fordilution—100 ml of ethoxypropanol were added.

Example 2

70 g of water were added dropwise with vigorous stirring at 65° C. to200 g of the product obtained as described in Example 1 (in the diluteform). After cooling to 40° C., another 130 ml of water were added. Theresulting dispersion had a mean particle size of 225 nm.

1-7. (canceled)
 8. A process for producing self-dispersing, curable,epoxy resins, the process comprising: (i) reacting (a) one or moreα,β-unsaturated carboxylic acid esters of the formula:R²R³C═C(R⁴)COOR¹   (I), wherein R¹ represents a hydrocarbon radicalhaving up to 15 carbon atoms, wherein R², R³, and R⁴ each independentlyrepresents a substituent selected from the group consisting of hydrogen,hydrocarbon radicals having up to 20 carbon atoms, and —(CH₂)_(n)—COOR¹,wherein R¹ is as defined above and n represents a number of from 0 to10; with (b) comprising at least one monoaminopolyalkylene oxidecompound having reactive hydrogen atoms of the formula:R⁸—O—R⁹—CH₂CH(R¹⁰)—NH₂   (II) wherein, R⁸ represents a monofunctionalorganic group having from 1 to 12 carbon atoms, R⁹ represents apolyoxyalkylene group having from 5 to 200 polyoxyalkylene unitsselected from the group consisting of ethylene oxide, propylene oxideand statistical or block mixtures thereof, and R¹⁰ represents hydrogenor an aliphatic radical having from 1 to 4 carbon atoms, and wherein (a)and (b) are present in quantities such that the equivalent ratio of thereactive hydrogen atoms in (b) to the α,β C═C double bonds in (a) isfrom 10:1 to 1:10, to form an intermediate product Z1; and (ii) reactingthe intermediate product Z1 with (c) one or more polyepoxides having anumber of oxirane rings, wherein the intermediate product Z1 and the oneor more polyepoxides are present in quantities such that the equivalentratio of the oxirane rings to the reactive hydrogen atoms in (b) is from100:1 to 1.5:1.
 9. The process according to claim 8, wherein the (a) oneor more α,β-unsaturated carboxylic acid esters of the formula (I)comprises a dialkyl maleate.
 10. The process according to claim 9,wherein the dialkyl maleate is selected from the group consisting ofdimethyl maleate, diethyl maleate and mixtures thereof.
 11. (canceled)12. (canceled)
 13. The process according to claim 8, wherein themono-aminopolyalkylene oxide compound has an average molecular weight offrom 148 to
 5000. 14. The process according to claim 8, wherein (a) and(b) are present in quantities such that the equivalent ratio of thereactive hydrogen atoms in (b) to the α,β C═C double bonds in (a) isfrom 4:1 to 1:4.
 15. The process according to claim 8, wherein theintermediate product Z1 and the one or more polyepoxides are present inquantities such that the equivalent ratio of the oxirane rings to thereactive hydrogen atoms in (b) is from 4:1 to 2:1.
 16. Aself-dispersing, hardenable epoxy resin, said epoxy resin produced bythe process according to claim
 8. 17. A self-dispersing, hardenableepoxy resin, said epoxy resin produced by the process according to claim9.
 18. A self-dispersing, hardenable epoxy resin, said epoxy resinproduced by the process according to claim
 11. 19. An aqueous dispersioncomprising a self-dispersing, hardenable epoxy resin according to claim16.
 20. The aqueous dispersion according to claim 19, wherein theself-dispersing, hardenable epoxy resin comprises dispersed particleshaving a mean particle size of 500 nm or less.